For example, vacuum pumps of the screw-rotor type are previously known from SE 0002129-5 (Svenska Rotor Maskiner AB). Screw-rotor pumps of that type comprises a compression section wherein intermeshing rotor bodies are rotated for compression of a gas that is drawn in between the rotating bodies. The compression section is driven by an expansion section having intermeshing rotor bodies that are caused to rotate through the expansion of a drive gas, such as compressed air, that is introduced in the expansion section.
Vacuum pumps of the ejector type, driven by compressed air for generating a sub-pressure, are previously known from SE 9800943-4 (PIAB AB), e.g. The ejector pump is driven by compressed air that is accelerated through a number of nozzles, arranged in succession. A pressure drop is generated about the jet of compressed air, between the nozzles, and used for evacuation of surrounding air that is drawn through openings in the ejector wall to be captured by the jet.
These two types of pumps have different operation characteristics. In this connection, the ejector is characterized by a fast initial effect within an upper pressure region below atmosphere, whereas the screw-rotor pump is characterized by a higher efficiency within a lower pressure region. Also, the screw-rotor pump is characterized by a considerable temperature rise in the compressed gas or air upon discharge from the compression section of the screw-rotor type pump.
Within the industries relying on vacuum operations, there is a desire to reduce the times required to evacuate a cavity, such as the volume of air that is defined under a suction cup. One method to satisfy this desire is to de-centralize the production of sub-pressure by spreading the vacuum sources to be positioned near the vacuum consumers, and thus omitting long passages for distribution of sub-pressure and reducing the total volume or air to be evacuated. However, in certain applications operated by sub-pressure, the elevated temperature in the compressed discharge air from a screw-rotor pump may obstruct a free de-centralization of vacuum sources. This applies, e.g., to the pharmaceutical and food industries, and the packing industry as well.
The present invention aims to meet the above desire and solve the problems referred to above by providing a vacuum pump comprising a screw-rotor pump in integration with an ejector, as defined in appended apparatus claim 1 and appended method claim 8.